1. Field of the Invention
The present invention relates to an ink composition used chiefly for printing by an inkjet system; in more detail, it relates to an ink composition of high printing quality and a method of recording a recording medium using this of excellent ink discharge stability and wherein clogging cannot occur, thereby preventing blurring.
2. Description of the Related Art
The inkjet recording method is a method of printing in which printing is performed by creating flying droplets of an ink composition, and depositing these on a recording medium such as paper. This method has the characteristic that it is capable of performing high-speed printing of a high-resolution, high-quality image with a comparatively inexpensive device. The ink compositions that are used in ordinary inkjet recording have water as their main constituent and contain therein coloring constituents and wetting agents such as glycerin with the object of preventing clogging.
However, with the previously proposed ink compositions, there was the problem that, when the ink permeated into the recording medium, blurring was sometimes produced, resulting in lowered printing quality. Blending with various types of surfactant was therefore proposed as a technique for producing an excellent image with no blurring, by accelerating or suppressing permeation of the ink composition into the recording medium.
For example, as prior art in which the use of an acid ester-based surfactant as surfactant is proposed, in Laid-open Japanese Patent Publication No. H. 5-59314, there is proposed an ink composition of short drying time obtained by combination of an aqueous liquid vehicle, coloring material, and phosphoric acid ester. Also, Laid-open Japanese Patent Publication No. H. 6-107971 proposes an aqueous pigment ink that does not produce liquid accumulations in the vicinity of the jets and that satisfies printing quality, by means of a recording liquid containing: a water-soluble solution, pigment, water-soluble resin, water and phosphoric acid ester-based surfactant or fluorine-containing surfactant; or boron-containing surfactant or polyoxyethylene alkyl ether or polyoxyethylene phenyl ether-based surfactant.
Furthermore, it has been proposed (Laid-open Japanese Patent Publication No. H. 6-106735) to obtain a high quality color image of high image density and no color blurring by employing in combination at least a color ink containing a surfactant or permeable solvent that confer permeability and a salt, and a black ink that thickens or coagulates due to the action of this salt. Specifically, an inkjet recording method is proposed whereby an excellent image is stated to be obtained by printing using the two liquids: a first liquid containing salt, and an ink composition.
Also, with an ink composition for inkjet recording, in addition to the property of producing excellent images with no blurring on the recording medium, it is required that discharge from the nozzle of the inkjet recording head should be achieved reliably and without deviating from the prescribed flight direction. If the ink fails to discharge or ink droplets are discharged deviating from the prescribed flight direction (hereinbelow, such deviation of ink droplets from the prescribed flight direction may be termed bending of the flight path of the ink droplets), this causes xe2x80x9cmissing dotsxe2x80x9d or lowering of sharpness of the image etc. Various proposals have been made involving adjusting the type and amount of additives of the ink composition in order to prevent such poor ink discharge and/or bending of the flight path. Several proposals have also been made for constructions of the inkjet recording head such as to reduce bending of the flight path. Regarding the latter, it has been proposed to attempt to ensure reliable discharge of ink droplets with no flight path bending for example by conferring on the nozzle plate the property of being resistant to wetting by the ink (ink repellence). For example, in Laid-open Japanese Patent Publication No. Sho. 57-107848, it is proposed to suppress leakage of ink around the nozzle by uniformly forming an ink repellent coating of for example fluorine resin on the inside surface of the nozzle and outside surface of the nozzle plate by sputtering. Furthermore, in Laid-open Japanese Patent Publication No. H. 7-125220, it is proposed to provide an ink repellent coating as far as the inside surface of the nozzle in a prescribed amount related to the amount of ink in the ink drop.
However, if, as in the prior art described above, a large quantity of surfactant is introduced into the ink composition, the solution stability of the ink composition is lowered, so a solid fraction clogs the ink discharging portions of the printer, resulting in the problems of poor stability of discharge and a tendency to clogging.
An object of the present invention is therefore to provide an ink composition with which there is no possibility of clogging, which is of excellent discharge stability, with which blurring is prevented, and whereby excellent images can be achieved.
A further object of the present invention is to provide a method of recording whereby a recording can be formed with which there is no possibility of clogging, which is of excellent discharge stability, with which blurring is prevented, and whereby excellent images can be achieved.
Also a further object of the present invention is to provide a recording with which there is no possibility of clogging, which is of excellent discharge stability, with which blurring is prevented, and whereby excellent images can be achieved.
The present inventors obtained the discovery that discharge stability of the ink drops and reliability in respect of clogging can be improved, blurring prevented and excellent printed images provided by including in combination a coloring agent, 2-pyrrolidone, a specific surfactant, a butyl ether-based solvent, water, and a water-soluble organic solvent.
Specifically, according to the present invention, the above objects are achieved by providing an ink composition containing at least a coloring agent, 2-pyrrolidone, a surfactant, a butyl ether-based solvent, water, and a water-soluble organic solvent wherein the surfactant is a chemical compound represented by the following chemical formula (I). 
Also, according to the present invention, there is provided an ink composition wherein the weight ratio of the surfactant, butyl ether-based solvent, and 2-pyrrolidone is 1:4:4 to 1:20:20.
Also, according to the present invention, there is provided an ink composition wherein the butyl ether-based solvent is triethylene glycol monobutyl ether.
Also, according to the present invention, there is provided an ink composition employed in an inkjet recording method using an inkjet recording head comprising a nozzle plate wherein some of the ink repellent coating layer that is coated onto the external surface of the nozzle plate is introduced on to the inner surface of the nozzle such that the volume of the gap within the nozzle from the outer surface of the nozzle plate as far as the meniscus-forming face is in a range of 0.05 to 0.50 with respect to the quantity of ink that is discharged.
Also, according to the present invention, there is provided an ink composition in which the added amount of the coloring agent is 1 to 5 weight % with respect to the ink composition.
Also, according to the present invention, there is provided an ink composition further containing dispersant.
Also, according to the present invention, there is provided an ink composition in which the dispersant is styrene-(meth)acrylic acid based water-soluble resin.
Also, according to the present invention there is provided an ink composition in which the water-soluble organic solvent has a boiling point of at least 180xc2x0 C.
Also, according to the present invention, there is provided an ink composition further containing as water-soluble organic solvent a tertiary amine.
Also, according to the present invention, there is provided an ink composition further containing alkali hydroxide, alginic acid derivative, or a sugar or sugar derivative.
Also, according to the present invention, there is provided an ink composition wherein the sugar derivative is a reduced sugar, oxidized sugar, sugar dehydration derivative, amino sugar, or thio-sugar.
Also, according to the present invention, there is provided an ink composition wherein the ink repellent coating layer is formed by co-deposition plating.
Also, according to the present invention, there is provided an ink composition as aforesaid further including a compound represented by the following chemical formula (II). 
Also, according to the present invention there is provided an ink composition wherein the content of the chemical compound represented by chemical formula (I) is at least 1 weight % of the total amount.
Also, according to the present invention, there is provided an ink composition wherein the content of the chemical compound represented by chemical formula (I) is 1 to 3 weight %.
Also, according to the present invention there is provided an ink composition wherein the content of the chemical compound represented by chemical formula (II) is at least 1 weight %.
Also, according to the present invention there is provided an ink composition wherein the butyl ether-based solvent is triethylene glycol monobutyl ether or diethylene glycol monobutyl ether.
Also, according to the present invention, there is provided an ink composition wherein the coloring agent is C. I. Pigment Yellow 128.
Also, according to the present invention, there is provided an ink composition wherein the content of the coloring agent is 15 weight % or less in the total amount of the ink composition, the content of the 2-pyrrolidone is at least 2 weight % in the total amount of the ink composition, and the content of the butyl ether-based solvent is at least 4 weight % in the total amount of the ink composition.
Also, according to the present invention, there is provided an ink composition further containing a polymeric dispersant having a carboxyl group in the molecule.
Also, according to the present invention, there is further provided an ink composition containing a moisture retaining agent selected from the group consisting of glycerin, diethylene glycol and ethylene glycol.
Also, according to the present invention there is provided a recording method wherein formation of a recording is performed by depositing the ink composition on the recording medium.
Also, according to the present invention, there is provided a recording method as aforesaid wherein printing is performed by discharging drops of the ink composition and depositing these drops on the recording medium.
Also, according to the present invention, there is provided a recording method as aforesaid employing an inkjet recording head comprising a nozzle plate that has been subjected to ink repellent treatment.
Also, according to the present invention, there is provided a recording method wherein formation of a recording is effected by filling a tank accommodating in its interior a foam comprising a porous member with the ink composition and discharging it from this tank to a recording head.
Also, according to the present invention, there is provided a recording wherein the ink composition is deposited in a prescribed pattern by the recording method.